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  // Match both null and undefined, but not zero, by using != null.

  // See https://stackoverflow.com/questions/2647867/how-to-determine-if-variable-is-undefined-or-null

  if (event.pageX != null && event.pageY != null) {

    return {x: event.pageX, y: event.pageY};

  }

  // pageX and pageY properties undefined. In those cases, the properties must

  // be retrieved from the event.originalEvent object instead.

  if (event.originalEvent && event.originalEvent.pageX != null && event.originalEvent.pageY != null) {

    return {x: event.originalEvent.pageX, y: event.originalEvent.pageY};

  }

  // Some old browsers do not support MouseEvent.pageX and *.pageY at all.

  // See https://developer.mozilla.org/en-US/docs/Web/API/MouseEvent/pageY

  // For those, we look at event.clientX and event.clientY instead.

  if (event.clientX == null || event.clientY == null) {

    // In some jQuery versions, some events created by jQuery do not have

    // clientX and clientY. But the original event might have.

    if (!event.originalEvent) {

      throw new Error("The event has no coordinates, and no event.originalEvent.");

    }

    event = event.originalEvent;

    if (event.clientX == null || event.clientY == null) {

      throw new Error("The original event has no coordinates.");

    }

  // Copied from jQuery.event.fix() in jQuery 1.4.1.

  // In newer jQuery versions, this code is in jQuery.event.mouseHooks.filter().

  var doc = document.documentElement, body = document.body;

  var pageX = event.clientX + ( doc && doc.scrollLeft || body && body.scrollLeft || 0 ) - ( doc && doc.clientLeft || body && body.clientLeft || 0 );

  var pageY = event.clientY + ( doc && doc.scrollTop  || body && body.scrollTop  || 0 ) - ( doc && doc.clientTop  || body && body.clientTop  || 0 );

  return {x: pageX, y: pageY};